Abstract
The aim of this project was to investigate a range of medicinal herbs which have radical scavenging and antioxidant activities and then apply novel mass spectrometric techniques to investigate and analyse active components responsible for their pharmaceutical actions.
A sensitive electron capture negative ionization of gas chromatography-mass
spectrometry (ECNI-GC-MS) method was developed to assess hydroxyl radical
production, as indicated by 3.4-dihydroxyphenylacetic acid (DOPAC) production,
which allows excellent evaluation of hydroxyl radical scavenging and antioxidant
activity of a number of medicinal Chinese herbs. Melatonin is an effective multiple
radical scavenger and antioxidant and has been used in this study for the comparison of
radical scavenging activity with medicinal herbs. To analyse active compounds from
herbal extracts, mass spectrometric techniques were used to separate components that
suppressed hydroxyl radical production from Dimocarpus longan Lour, determine
known ginsenosides from ginseng extracts as well as to identify and quantify melatonin
in ten herbal extarcts.
The results obtained indicated that 1) the utilization of alumina in the ECNI-GC-MS
method diminished interferences from “noise” products in a Fenton-type reaction,
which allows obtaining pure final hydroxyl radical product and this method
demonstrated optimal sensitivity and reliability; 2) Aqueous extracts of all herbs
analysed showed different levels of hydroxyl radical scavenging activity. Dimocarpus
longan Lour, Chrysanthemum morifolium Ramat, Lonicera hypoglauca Miq, Ginkgo biloba L, Rehmannia flutinosa and Libosch Cornus officinalis Sieb all exhibited
stronger inhibitory effect on hydroxyl radical production than melatonin. 3) Aqueous
extract of Dimocarpus longan Lour. showed the greatest inhibitory effect on hydroxyl
radical production among the other herbs tested. The active fractions of this herb eluted
just after the void volume using HPLC suggesting that the active compounds
responsible for radical scavenging activity are polar and water soluble. They may
belong to phenol group of chemicals. 4) Herbal extracts using non-polar solvents
showed no effect on hydroxyl radical production suggesting active compounds in those
herbs are water soluble. 5) Different species and origins of ginseng were compared for
their radical scavenging activity. Chinese fresh ginseng (Oriental ginseng) showed
higher activity than Korean ginseng tablet and American ginseng. Seven known active
ginsenosides were identified using HPLC-MS-MS. 6) Melatonin was found at varying
concentrations in ten herbs, which may contribute to the radical scavenging activity of
herbs, on the other hand, it may provide the justification of clinical use and food
resources, particularly for those herbs contain high level of melatonin.